1. Field of the Invention
The present invention relates to a driving method for a plasma display panel (PDP). More specifically, the present invention relates to a PDP driving method for improving the ability to represent low gray scales.
2. Discussion of the Related Art
A PDP is a flat display panel that shows characters or images using plasma generated by gas discharge. PDPs may include millions of pixels in a matrix format, where the PDP's size determines the number of pixels. Referring to FIG. 1 and FIG. 2, a typical PDP structure will now be described.
FIG. 1 shows a partial perspective view of a PDP, and FIG. 2 schematically shows a PDP electrode arrangement.
As shown in FIG. 1, the PDP includes glass substrates 1 and 6 sealed together with a predetermined gap therebetween. Scan electrodes 4 and sustain electrodes 5 are formed in parallel pairs on the glass substrate 1, and they are covered with a dielectric layer 2 and a protection film 3. A plurality of address electrodes 8 is formed on the glass substrate 6, and they are covered with an insulating layer 7. Barrier ribs 9 are formed on the insulating layer 7 between the address electrodes 8, and phosphors 10 are formed on the surface of the insulating layer 7 and between the barrier ribs 9. The glass substrates 1 and 6 are provided facing each other with discharge spaces 11 formed between them. A portion of the discharge space 11 between an address electrode 8 and a crossing part of a pair of a scan electrode 4 and a sustain electrode 5 forms a discharge cell 12.
As shown in FIG. 2, the PDP electrodes have an n×m matrix format. The address electrodes A1 to Am are arranged in the column direction, and n scan electrodes Y1 to Yn and n sustain electrodes X1 to Xn are arranged in pairs in the row direction.
A subfield in the typical PDP driving method includes a reset period, an address period, a sustain period, and an erase period (waveforms within a subfield will be described for ease of description.)
In the reset period, charge states of the display cells are reset so that address operations may be effectively performed. In the address period (also known as a scan period or a write period), cells which are to be turned on are selected, and wall charges are accumulated in the selected cells (addressed cells). In the sustain period, a discharge for displaying actual images is performed. In the erase period, the wall charges on the cells are reduced, and the sustain discharge is terminated.
FIG. 3 shows a conventional PDP driving waveform and a quantity of light emitted by a subfield.
As shown in the conventional PDP driving method, a minimum unit of light, is a light of the subfield with a weight of 1. It is represented as the sum of the light generated during the address period, the sustain period, and the reset period of the second subfield, which is immaterial. In other words, in the period of the first subfield, an address discharge (address light) forms positive wall charges at the scan electrode in the address period. The voltage at the scan electrode Y is set higher than the voltage at the sustain electrode X, to apply a sustain discharge voltage of Vs between them, thereby performing a sustain discharge (sustain light) in the sustain period. Next, the minimum unit of light is represented through a reset operation of the reset period of the second subfield. In this instance, the light emitted in the reset period is a bit less, so it is immaterial. The light for representing the second subfield (the weight of 2) is represented through the address discharge (address light) and the three sustain discharges (the sustain discharge voltage of Vs alternately applied to the scan electrode Y and the sustain electrode X) in the sustain period.
Therefore, since the minimum unit of light in the conventional PDP driving method includes light generated from an address discharge (address light) and a sustain discharge (sustain light), it is restricted in realizing the lower brightness. Further, since high Xe is currently used to increase emission efficiency, which increases the light generated by a single sustain discharge, a much lower minimum unit of light may be required to increase the representation performance of the low gray scales. Also, big differences of the representation performance of the low gray scales may be generated according to the brightness per sustain discharge pulse when representing low gray scales with few sustain discharge pulses.